Figure 4.

Brief tetanic stimulation causes glutamatergic heterosynaptic inhibition in the mossy fiber system. Two pairs of stimulating electrodes were inserted into the dentate gyrus, and the mossy fiber response was recorded with an extracellular field electrode in CA3 stratum lucidum. (A) Brief trains of stimuli to one pathway were used to produce glutamate spillover onto the other pathway. (B) The amplitude of the fEPSP plotted over time. The response to the conditioned stimulus (•) is depressed compared with the unconditioned stimulus (○). This depression disappears during the application of MCPG. The results of six experiments are summarized in C₁ and the average of these experiments is shown in C₂. Depression is calculated as percentage of unconditioned response.